[⁸⁹Zr]Zr-rituximab PET/CT activity in patients with therapy refractory interstitial pneumonitis: a feasibility study

Recent studies on immune-mediated inflammatory lung diseases show encouraging treatment results with rituximab, a monoclonal antibody (mAb) against CD20-expressing B lymphocytes. The present pilot study aimed to explore the possibility to image CD20-expression in the lungs as future early predictor of treatment response. We describe a series of 10 patients with therapy refractory interstitial pneumonitis who were treated with rituximab (1000 mg at day 0 and day 14) and underwent PET/CT after the administration of [⁸⁹Zr]Zr-N-suc-DFO-rituximab abbreviated as [⁸⁹Zr]Zr-rituximab. [⁸⁹Zr]-rituximab PET/CT of the chest was performed on day 3 and 6. [⁸⁹Zr]Zr-rituximab PET/CT showed visual and quantifiable increased pulmonary activity in four patients. Other patients demonstrated no increased activity in the lungs. One patient developed a severe allergic reaction during infusion of the first 10% unlabeled rituximab after which rituximab infusion was ceased. Subsequent administration of [⁸⁹Zr]Zr-rituximab, however, did not result in any adverse reaction. This patient demonstrated the highest uptake of [⁸⁹Zr]Zr-rituximab in mediastinal lymph nodes and lung parenchyma compared to the other 9 patients who did receive the full dose rituximab before [⁸⁹Zr]Zr-rituximab. This pilot study demonstrates that [⁸⁹Zr]Zr-rituximab PET/CT imaging in patients with therapy refractory interstitial pneumonitis is feasible and shows lung-specific uptake in some patients. Further research with larger sample size should establish if the [⁸⁹Zr]Zr-rituximab uptake correlates with treatment response to rituximab. The higher uptake in the absence of a full 1000 mg rituximab preload may suggest that future studies should consider [⁸⁹Zr]Zr-rituximab imaging at low mAb dose before treatment with rituximab.